A postcard or post card is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope. In some places, it is possible to send them for a lower fee than for a letter. Stamp collectors distinguish between postcards (which require a stamp) and postal cards (which have the postage pre-printed on them). While a postcard is usually printed by a private company, individual or organization, a postal card is issued by the relevant postal authority. The United States Postal Service defines a postcard as: rectangular, at least 3+1⁄2 inches (88.9 mm) high × 5 inches (127 mm) long × 0.007 inches (0.178 mm) thick and no more than 4+1⁄4 inches (108 mm) high × 6 inches (152.4 mm) long × 0.016 inches (0.406 mm) thick. However, some postcards have deviated from this (for example, shaped postcards).

The study and collecting of postcards is termed deltiology.
In 1861, John P. Charlton of Philadelphia patented the postcard, selling the rights to H. L. Lipman, whose postcards, complete with a decorated border, were labeled "Lipman's postal card." Then in 1873, Post Master John Creswell, introduced the first pre-stamped "penny postcards". These first postcards depicted Interstate Industrial Exposition that took place in Chicago. The postcards were made because people were looking for an easier way to send quick notes. The first postcard to be printed as a souvenir in the United States was created in 1893 to advertise the World's Columbian Exposition in Chicago.
The Post Office was the only establishment allowed to print postcards, and it held its monopoly until May 19, 1898, when Congress passed the Private Mailing Card Act which allowed private publishers and printers to produce postcards. Initially, the United States government prohibited private companies from calling their cards “postcards,” so they were known as “souvenir cards.” These cards had to be labeled "Private Mailing Cards". Although this prohibition was rescinded in December 24th, 1901, when private companies could use the word "postcard". Postcards were not allowed to have a divided back and correspondants could only write on the front of the postcard. This was known as the "undivided back" era of postcards. On March 1st, 1907 the Post Office allowed private citizens to write on the address side of a postcard. It was on this date that postcards were allowed to have a "divided back".
 
Back of the above 1905 cardOn these cards the back is divided into two sections, the left section being used for the message and the right for the address. Thus began the Golden Age of American postcards, which lasted until 1915, when World War I blocked the import of the fine German-printed cards.
Postcards, in the form of government postal cards and privately printed souvenir cards, became very popular as a result of the Columbian Exposition, held in Chicago in 1893, after postcards featuring buildings were distributed at the fair. In 1908, more than 677 million postcards were mailed.
The "white border" era, named for obvious reasons, lasted from about 1916 to 1930. The "linen card" era lasted from about 1931 to the early 1950s, when cards were primarily printed on papers with a textured surface similar to linen cloth. The last and current postcard era, which began about 1939, is the "chrome" era, however these types of cards didn't begin to dominate until about 1950. The images on these cards are generally based on colored photographs, and are readily identified by the glossy appearance given by the paper's coating.
In 1973 the British Post Office introduced a new type of card, PHQ Cards, popular to collectors, especially when they have the appropriate stamp affixed and a First day of issue postmark obtained.

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Petrified Forest National Park is a United States national park in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about 146 square miles (380 km2), encompassing semi-desert shrub steppe as well as highly eroded and colorful badlands. The park's headquarters is about 26 miles (42 km) east of Holbrook along Interstate 40 (I-40), which parallels the BNSF Railway's Southern Transcon, the Puerco River, and historic U.S. Route 66, all crossing the park roughly east–west. The site, the northern part of which extends into the Painted Desert, was declared a national monument in 1906 and a national park in 1962. About 600,000 people visit the park each year and take part in activities including sightseeing, photography, hiking, and backpacking.

Averaging about 5,400 feet (1,600 m) in elevation, the park has a dry windy climate with temperatures that vary from summer highs of about 100 °F (38 °C) to winter lows well below freezing. More than 400 species of plants, dominated by grasses such as bunchgrass, blue grama, and sacaton, are found in the park. Fauna include larger animals such as pronghorns, coyotes, and bobcats; many smaller animals, such as deer mice; snakes; lizards; seven kinds of amphibians, and more than 200 species of birds, some of which are permanent residents and many of which are migratory. About half of the park is designated wilderness.

The Petrified Forest is known for its fossils, especially fallen trees that lived in the Late Triassic, about 225 million years ago. The sediments containing the fossil logs are part of the widespread and colorful Chinle Formation, from which the Painted Desert gets its name. Beginning about 60 million years ago, the Colorado Plateau, of which the park is part, was pushed upward by tectonic forces and exposed to increased erosion. All of the park's rock layers above the Chinle, except geologically recent ones found in parts of the park, have been removed by wind and water. In addition to petrified logs, fossils found in the park have included Late Triassic ferns, cycads, ginkgoes, and many other plants as well as fauna including giant reptiles called phytosaurs, large amphibians, and early dinosaurs. Paleontologists have been unearthing and studying the park's fossils since the early 20th century.

The park's earliest human inhabitants arrived at least 8,000 years ago. By about 2,000 years ago, they were growing corn in the area and shortly thereafter building pit houses in what would become the park. Later inhabitants built above-ground dwellings called pueblos. Although a changing climate caused the last of the park's pueblos to be abandoned by about 1400 CE, more than 600 archeological sites, including petroglyphs, have been discovered in the park. In the 16th century, Spanish explorers visited the area, and by the mid-19th century a U.S. team had surveyed an east–west route through the area where the park is now located and noted the petrified wood. Later roads and a railway followed similar routes and gave rise to tourism and, before the park was protected, to large-scale removal of fossils. Theft of petrified wood remains a problem in the 21st century.

The Painted Desert is a United States desert of badlands in the Four Corners area from the Grand Canyon National Park into the Petrified Forest National Park. Much of the area within the Petrified Forest National Park is protected as the Petrified Forest National Wilderness Area. Much of the Painted Desert region is within the Navajo Nation.

Geology
The desert is composed of stratified layers of easily erodible siltstone, mudstone, and shale of the Triassic Chinle Formation. These fine grained rock layers contain abundant iron and manganese compounds which provide the pigments for the various colors of the region. Thin resistant lacustrine limestone layers and volcanic flows cap the mesas. Numerous layers of silicic volcanic ash occur in the Chinle and provide the silica for the petrified logs of the area. The erosion of these layers has resulted in the formation of the badlands topography of the region.

In the southern portions of the desert the remains of a Triassic period coniferous forest have fossilized over millions of years. Wind, water and soil erosion continue to change the face of the landscape by shifting sediment and exposing layers of the Chinle Formation. An assortment of fossilized prehistoric plants and animals are found in the region, as well as dinosaur tracks and the evidence of early human habitation.